Contents
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What is CMOS
NMOS
PMOS
Working of CMOS
Advantages of CMOS
Disadvantages of CMOS
Applications of CMOS
Types of CMOS logic gates
What is CMOS:
• CMOS (Complementary Metal Oxide
Semiconductor) is a combination
of NMOS and PMOS transistors and it is a voltagecontrolled four-terminal device.
• The terminals are Gate , Source , Drain and Substrate(body).
• The NMOS and PMOS are the types of Metal Oxide
Semiconductor Field Effect Transistors (MOSFET).
• The importance of CMOS in semiconductor
technology is its low power dissipation and low
operating currents.
• The output impedance of MOSFET is more because
NMOS:
The symbol of the NMOS transisitor
• The n-channel MOSFET is called NMOS.
• It has a substrate of p-type, which consists of
majority carriers are holes.
• The n-channel consists of majority carriers are
electrons.
• The flow of electrons is fast as compared to holes.
• Hence, NMOS transistors are more rapid than
PMOS transistors
PMOS:
The symbol of the PMOS transistor
• The p-channel MOSFET is called PMOS.
• It has a substrate of n-type, which consists of majority
carriers are electrons.
• When a negative voltage is applied to the gate end of the
PMOS, it repels the electrons.
• The attraction of holes results in the formation of the
channel called the p-channel.
• The channel is formed between the source and drain.
Working of CMOS:
• The structure consists of the NMOS transistor inverted
on the top of the PMOS transistor.
• The substrate is of the P-type, and three N++ regions.
• The two N++ regions are small and the third N++ region
is large.
• The two smaller regions are a part of the NMOS
transistor, while the third N++ region is a part of the
PMOS transistor.
• The two P++ regions are diffused into the larger N++
region to form the PMOS transistor.
• The top surface is protected and covered using the
Working of CMOS:
• CMOS has the least amount of power dissipation in the
switching applications.
• It is because when one transistor is OFF, the other
becomes ON.
• For example, if PMOS is ON, the NMOS transistor will
be OFF.
Working of CMOS:
• Let's consider the two states of the CMOS, when the input
voltage (A) is 0.
• A in the above diagram is the input voltage that is fed to
the NMOS and PMOS transistors.
• When the input voltage (A) = 0V, the PMOS conducts, and
NMOS will remain in the OFF, A' will become 1 when A is 0.
• PMOS is strong passer of 1 because the PMOS switch is
closed and the NMOS switch at the bottom is open.
Working of CMOS:
• When the input voltage A = 1, A' will be 0. In such a
state, the PMOS will be OFF, and NMOS will conduct.
• It means that the output is 0 when the input is 1.
• NMOS is strong passer of 0 because the PMOS switch
at the top is open and the NMOS switch is conduct.
Advantages of CMOS:
The advantages
Semiconductors:
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of
Complementary
Metal
Oxide
Very low power dissipation
Reduced circuit complexity
Produces very less heat
Low static power Consumption
Temperature stability
Improved noise immunity
High fan-out
MOSFETs operate at greater efficiency at lower
voltages.
Disadvantages of CMOS:
The disadvantages of Complementary Metal Oxide
Semiconductors:
• MOSFETs are vulnerable to damage by electrostatic
charges due to the thin oxide layer.
• Overload voltages make MOSFETs unstable.
Applications of CMOS:
The applications
Semiconductors:
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of
Complementary
Metal
Oxide
Integrated Circuits
Chip designing
Microprocessor designing
ASIC designing
CPU Memories
Radiofrequency applications use MOSFET amplifiers
extensively.
• Power MOSFETs can be used to regulate DC motors.
• MOSFETs are used in the design of the chopper circuit.
Types of CMOS logic gates
The Complementary Metal Oxide Semiconductors are
categorized as:
• CMOS Inverter
• CMOS NAND
• CMOS NOR
• CMOS Operational Amplifiers
Thank You